The present invention relates to a reaction hydraulic turbine draft tube. In particular, the present invention relates to elbow type draft tubes having a splitter vane.
In a reaction hydraulic turbine, a draft tube is the portion of the flow passage between the exit of the turbine runner and the exit of the turbine. The purpose of the draft tube in a reaction hydraulic turbine is to recover a portion of the energy left in the flow at the runner exit. The draft tube outlet cross-sectional area is larger than that at the inlet. This results in typically lower outlet velocities than inlet velocities. It is desirable to minimize the kinetic energy left in the flow at the exit of the draft tube since most of this energy is lost when the flow exits the draft tube.
Many draft tubes must turn the flow by 90 degrees or more, since the draft tube inlet flow is typically vertical and the outlet flow is typically horizontal. In small turbines the flow may be opposite. Such draft tubes are commonly known as elbow type draft tubes.
One of the problems inherent in many previous draft tube designs is that the flow can separate from the profile of the draft tube as it is being redirected. This flow separation can result in a substantial loss in the efficiency of the turbine. Splitter vanes, sometimes called flow splitters, have been used in the past to improve the performance of poor draft tube designs. Poor performance is especially noticeable at operating points where the flow rate is greater than the flow rate at the peak efficiency point for a given head.
The conventional splitter vane extends across the entire width of the draft tube and is anchored in the draft tube side walls. The splitter vane is located in the draft tube adjacent the elbow to force the water fluid passing through the draft tube to change direction. Such a splitter vane for an elbow shaped draft tube is disclosed in U.S. Pat. No. 1,467,168 issued Sep. 4, 1923 to Victor Kaplan. Alternatively, U.S. Pat. No. 2,060,101 issued Nov. 10, 1936 to Lewis Moody discloses mounting the flow splitter vane across the draft tube and anchoring the flow splitter to the side walls of the draft tube and a central pier extending longitudinally along the draft tube.
While the use of flow splitter vanes improves performance, such flow splitter vanes do not facilitate the natural swirling flow of the water through the draft tube. The longitudinal extending piers further compound this problem. The flow at the exit of a turbine runner is by nature a typically swirling flow especially at flow rates below the flow rate corresponding to the peak efficiency for a given operating head. The use of a conventional splitter vane results in a decrease in draft tube efficiency for these part load conditions due to the resulting blockage of the swirl component of the flow. The conventional splitter vane is not feasible for large turbines since it results in a very large structure subject to very high static and dynamic loads due to the large surface area of the splitter vane extending across the entire width of the draft tube and impeding the natural swirl or vortex flow through the draft tube at flow rates below peak efficiency.
There is a need for a draft tube having a flow splitter vane that does not result in any efficiency decrease for flow rates below peak efficiency flow rates and that still provides the full benefits at flow rates above the peak efficiency flow rate for a given head.
The present invention relates to a splitter vane mounted within an elbow shaped draft tube of a reaction hydraulic turbine that partially extends across the width of the draft tube to redirect flow about said elbow in the draft tube. The splitter vane has opposing side edge surfaces spaced from the side walls of the draft tube to permit swirl flow around the splitter vane within the draft tube. Such a splitter vane is referred to throughout the disclosure as a xe2x80x9cpartial splitter vanexe2x80x9d.
The partial splitter vane of the present invention does not extend across the full width of the draft tube allowing the peripheral flow to swirl around the splitter as it moves through the draft tube.
The partial splitter vane does not result in any efficiency decrease for these operating conditions below peak efficiency flow rates and still provides the full benefits at flow rates above the peak efficiency flow rate for a given head.
The partial splitter vane is significantly smaller than a conventional splitter vane that extends across the entire width of the draft tube and this results in much lower static and dynamic loads due to its smaller surface area and minimal blockage of the swirl component of the flow by the partial splitter vane. This makes it feasible to use a partial splitter vane on large turbines as well as small turbines.
In accordance with the present invention the splitter vane may extend across less than about 80% of the width of the draft tube. Preferably the width of the splitter vane extends between 50 and 80 percent of the width of the draft tube and has its opposing side edges spaced substantially the same distance from an adjacent one of the side walls of the draft tube. The opposing side edge surfaces of the splitter vane may diverge from one another in the direction of flow towards the outlet of the draft tube.
Preferably, the draft tube includes a plurality of support posts embedded at one end in the draft tube and connected at the other end to position the splitter vane in non-contacting relation with the side walls of the draft tube. Preferably the support posts are mounted to a lower surface of the splitter vane. The support posts are surrounded by tubes shaped to minimize the effects of the posts on the flow within the draft tube. The draft tube preferably includes at least one pier adjacent the outlet extending into the draft tube. Preferably, the splitter vane further includes at least one pier receiving recess adapted to receive the pier and to support the splitter vane on the pier. In the preferred embodiment the splitter vane is offset across the width of, and to one side of, the draft tube.
In accordance with one aspect of the present invention there is provided a draft tube for use in a turbine having a turbine runner. The draft tube comprises side walls having an inlet for positioning adjacent the turbine runner and an outlet defining a flow exit for the turbine. The side walls of the draft tube diverge in width between the inlet and the outlet. The draft tube has a curved elbow to position the outlet substantially perpendicular to the inlet. The draft tube has a splitter vane mounted within the draft tube extending about the elbow and partially extending across the width of the draft tube to redirect flow about said elbow in the draft tube. The splitter vane has opposing side edge surfaces spaced from the side walls to permit swirling flow around the splitter vane within the draft tube.
The present invention is directed to a reaction hydraulic turbine that includes a draft tube having side walls arranged to define an inlet and an outlet and an elbow arranged to position the outlet substantially perpendicular to the inlet. A turbine runner is positioned adjacent the inlet and the outlet being arranged to define a flow exit, and a splitter vane is mounted within the draft tube to partially extend across a width of the draft tube, so that flow is redirected about the elbow of the draft tube. The splitter vane has opposing side edge surfaces that are spaced from the side walls, such that swirl flow is permitted around the splitter vane within the draft tube.
In accordance with a feature of the invention, the draft tube has a diverging width between the inlet and the outlet.
According to another feature of the invention, the splitter vane extends across less than about 80% of the width of the draft tube.
Further, the opposing side edge surfaces of the sputter vane are arranged to diverge from one another in a flow direction toward the outlet.
The width of the splitter vane extends between 50% and 80% the width of the draft tube and the opposing side edges are spaced substantially a same distance from respective adjacent side walls of the draft tube.
Moreover, the draft tube further includes a plurality of support posts, in which one end of the plurality of support posts are embedded in the draft tube and an other end of the plurality of support posts are connected to the splitter vane to position the splitter vane in non-contacting relation with the side walls of the draft tube. The plurality of support posts are surrounded by tubes shaped to minimize effects of the plurality of posts on the flow within the draft tube. The support posts are mounted to a lower surface of the splitter vane.
The reaction hydraulic turbine further includes at least one pier positioned adjacent the outlet and to extend into the draft tube and a plurality of support posts having one end embedded in the draft tube and an other end connected to position the splitter vane in the draft tube. The splitter vane further includes at least one recess structured and arranged to receive the at least one pier, such that the splitter vane is supported on the pier. The support posts are surrounded by tubes shaped to minimize effects of the posts on the flow within the draft tube. The support posts are mounted to a lower surface of the splitter vane.
In accordance with a further feature of the present invention, the splitter vane is mounted offset across the width of the draft tube.
The present invention is directed to an apparatus including an elbow tube having an inlet end and an outlet end, and a splitter vane comprising vane edges spaced from an interior surface of the elbow tube.
According to a feature of the invention, the elbow tube has an interior width that increases between the inlet and the outlet.
Further, in a region of the splitter vane, a width of the interior surface increases. The splitter vane is structured to substantially correspond to the width increase of the interior surface.
In accordance with another feature of the instant invention, the splitter vane extends across less than 80% of an interior width in a region of the splitter vane. Further, the splitter vane extends across more than 50% of the interior width in the region of the splitter vane.
According to still another feature of the present invention, the vane edges are arranged to diverge from each other in a flow direction.
The apparatus further includes at least one support post arranged to couple the splitter vane to the elbow tube. The at least one support post is surrounded by a tube structured to minimize effects of on a flow within the elbow tube.
The apparatus further includes at least one pier coupled to an end of the splitter vane adjacent the outlet. The at least one pier is structured and arranged to extend through the outlet. Further, the splitter vane includes at least one recess structured and arranged to receive the at least one pier. Still further, at least one support post is arranged to couple the splitter vane to the elbow tube. The at least one support post is surrounded by a tube structured to minimize effects of on a flow within the elbow tube.